The present invention relates to a transmission housing arrangement of a transmission in an automobile, and particularly to a transmission housing arrangement comprising a main housing accommodating a plurality of meshing gears and an extension housing accommodating the additional meshing gears. The present invention relates for example to a transmission housing arrangement of a multi-speed transmission.
In conventional transmission housings of this type, a main housing contains some of the meshing gears, of the transmission and an extension housing connected to the main housing contains the additional meshing gears of the transmission. An intermediate plate is used to partition the extension housing from the main housing. The intermediate plate has a through hole at a lower portion thereof for connecting the extension housing to the main housing. In this way, lubricating oil in the main housing can be introduced through the through hole into the extension housing and lubricating oil in the extension housing can be drained through the through hole into the main housing. A space is provided under the meshing gear in the extension housing communicates with the through hole so the lubricating oil flows smoothly between the through hole and the space under the meshing gear in the extension housing. Problems occur in transmission systems of this type because as the meshing gear in the extension housing rotates, it tends to sweep lubricating oil up toward the gears. Since there is a smooth flow between the through hole and the room under the meshing gear a large amount of lubricating oil flows from the main housing into the extension housing. As a result, if only a normal amount of lubricating oil is filled into the transmission housing, the meshing gears in the main housing will lack the required amount of lubricating oil resulting in a poor transmission efficiency. On the other hand, if an excessive amount of lubricating oil is filled into the extension housing, (i.e. when too much oil is filled into the transmission housing) fluid friction between the meshing gears in the extension housing and the lubricating oil will also lower the transmission efficiency.